A vehicle's engine may drive accessories including an air conditioning compressor, alternator, power steering pump, and vacuum pump. The accessories may be driven from the engine's crankshaft via a belt and pulley system located at the front side of the engine. During some conditions, fuel flow to engine cylinders may be ceased to conserve fuel. The accessories may continue to receive power from the vehicle's wheels while the engine spins. If the vehicle includes an automatic transmission with torque converter, the torque converter's lockup clutch may be fully closed while the vehicle is decelerating. The vehicle's kinetic energy may be delivered to the engine via the transmission and vehicle wheels when the torque converter clutch is locked. However, a significant portion of the vehicle's kinetic energy may be consumed by rotating the engine, which may not provide useful work. Further, the vehicle may not coast as far as is desired when the vehicle's kinetic energy is used to rotate the unfueled engine. Consequently, a significant portion of the vehicle's kinetic and potential energy may be lost. In addition, the additional torque to spin and accelerate the engine may lead to reduced occupant comfort levels during vehicle deceleration and downshifting. Having so accelerate a large inertia (like an engine) during a downshift may lead to a “head bob,” a short-lived vehicle deceleration that may be produced when a large rotating inertia is accelerated by the vehicle's kinetic energy.
The inventors herein have recognized the above-mentioned issues and have developed a method for operating a driveline of a vehicle, comprising: unlocking a torque converter clutch and driving on-board vehicle accessories via an accessory drive coupled to a driveline at or downstream of a torque converter turbine and upstream of a transmission gear clutch in response to a request to drive the on-board vehicle accessories and decelerate a vehicle in a first mode.
By unlocking a torque converter in response to a request to decelerate a vehicle and drive on-board vehicle accessories, an engine may be effectively decoupled from a driveline so that the driveline may continue to rotate without having to rotate the engine. In particular, a torque converter transmits little torque from vehicle wheels to an engine when the torque converter's lockup clutch is open. Consequently, a higher portion of a vehicle's potential and kinetic energy may be used to drive vehicle accessories instead of rotating an engine. Further, a greater portion of the vehicle's kinetic and potential energy may be used to coast the vehicle to a location down a road the vehicle is traveling. However, if increased driveline braking is desired to maintain vehicle speed down an incline, the torque converter clutch may be locked to provide engine braking to the driveline.
The conventional way of configuring an engine puts the accessories on the front of the engine upstream of the engine and transmission. This configuration has the disadvantage of having to spin the engine with all of it frictional losses to power the accessories from the vehicle's kinetic energy. The invented arrangement allows this the engine to rotate with the accessories while allowing other modes of operation where spinning the engine with the accessories is not required. Thus, the accessories can be driven by the engine alone or the vehicle's kinetic energy alone. Additional favorable control modes may be provided based on this capability.
The present description may provide several advantages. For example, the approach may increase vehicle driveline efficiency. Additionally, the approach may increase vehicle fuel economy. Further, the approach may increase recovery of a vehicle's potential and kinetic energy.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.